Method and a device for damping flow pulsations in hydrostatic hydraulic machines of the displacement type

Abstract

Each cylinder of a hydrostatic hydraulic machine of the displacement type is preliminarily pressurized after the inlet port of the cylinder has been exposed to the low pressure side of the machine and before the inlet port of the cylinder is exposed to the high pressure side of the machine. The preliminary pressurization is effected by use of a separate pressure chamber containing a pressurized fluid that is rapidly discharged into the inlet port of each cylinder before the cylinder inlet port is exposed to the high pressure side of the machine. The separate pressure chamber is recharged from the high pressure side of the machine at a rate that is slower than the rate at which pressurized fluid is discharged from the chamber into the inlet port of a cylinder.

Having thus described the invention we claim: 
     
       1. In a hydrostatic machine of the displacement type comprising a plurality of cylinders each of which has an inlet port, a pressure control device comprising a pair of spaced control ports that are connected respectively to a high pressure side and a low pressure side of said machine, means for effecting relative motion between said inlet ports of said cylinders and said control ports of said pressure control device to successively expose said cylinders to the low and high pressure sides of said machine, and means for effecting a preliminary pressurization of each cylinder before the inlet port of said cylinder is exposed to the high pressure side of said machine, the improvement wherein said preliminary pressurization means comprises a pressure chamber separate from the high pressure and low pressure sides of said machine, means for rapidly discharging a pressurized fluid from said pressure chamber into the inlet port of each cylinder after said inlet port of said cylinder has been exposed to the low pressure side of said machine and before said inlet port is exposed to the high pressure side of said machine, and means for charging pressurized fluid into said pressure chamber at a rate that is slower than the rate at which pressurized fluid is discharged from said pressure chamber into the inlet port of a cylinder, the difference in the charging and discharging rates of said pressurized fluid into and out of said pressure chamber being operative to reduce the generation of noise and vibration resulting from operation of the hydrostatic machine. 
     
     
       2. The machine of claim 1 wherein said charging of pressurized fluid into said pressure chamber occurs simultaneously with the discharge of pressurized fluid from said chamber into the inlet port of a cylinder. 
     
     
       3. The machine of claim 1 wherein said means for discharging pressurized fluid from said pressure chamber comprises an auxiliary port in said pressure control device, and a first duct connecting said pressure chamber to said auxiliary port, said means for charging pressurized fluid into said pressure chamber comprising a second duct connecting said pressure chamber to the high pressure side of said machine, the effective cross sectional area of said second duct being smaller than the effective cross sectional area of said first duct. 
     
     
       4. The machine of claim 3 wherein the effective cross sectional area of said second duct is defined by a restriction in said second duct. 
     
     
       5. The machine of claim 1 wherein said cylinders are mounted in a cylinder drum for rotation about a central bearing shaft, said pressure chamber being disposed within said bearing shaft. 
     
     
       6. The machine of claim 1 wherein said charging of pressurized fluid into, and said discharge of pressurized fluid from, said pressure chamber occur receptively during different time periods. 
     
     
       7. The machine of claim 1 wherein said means for discharging pressurized fluid from said pressure chamber comprises an auxiliary port located in said pressure control device between said pair of spaced control ports, the inlet port of each cylinder being shaped to define a first portion which communicates with said control ports and at least one further portion which communicates with said auxiliary port during said relative motion between said cylinder inlet ports and said pressure control device. 
     
     
       8. The machine of claim 7 wherein said further portion of said inlet port comprises at least tow circumferentially spaced recesses in a wall of said inlet port.